The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIGS. 1-3C, wireless network devices typically transmit and receive radio frequency (RF) signals via RF transceivers. FIG. 1 shows a RF transceiver. FIG. 2 shows RF signals including wanted and unwanted RF signals that an RF transceiver may receive via a source such as an antenna. FIGS. 3A and 3B show different configurations of RF transceivers that can simultaneously transmit and receive RF signals. FIG. 3C shows a duplexer that may be a source of unwanted RF signals.
In FIG. 1, an RF transceiver 100 that transmits and receives RF signals in wireless communication systems is shown. The RF transceiver 100 may transmit and receive RF signals in a desired frequency band. The RF transceiver 100 may comprise a transmitter 102 that transmits RF signals and a receiver 104 that receives RF signals via an antenna 106. The transmitter 102 may be a super-heterodyne transmitter, a direct conversion transmitter, or other suitable transmitter. The receiver 104 may be a super-heterodyne receiver, a direct conversion receiver, or other suitable receiver. The RE transceiver 100 may be implemented by an integrated circuit (IC).
Transmitters and receivers generate unwanted signal components called intermodulation components due to non-linearity of circuit blocks. For example, receivers may generate intermodulation components due to non-linearity of low-noise amplifiers, transconductors, mixers, amplifiers, and filters. Mixers are a significant source of nonlinearity, particularly in direct conversion receivers.
When receivers receive a wanted channel at a small power level together with unwanted signals with relatively larger power, intermodulation components may fall on or near the wanted channel and reduce receiver performance. Receivers typically use mixers to convert input signals associated with one carrier frequency to output signals having another carrier frequency called an intermediate frequency (IF) or to baseband as in receivers employing direct conversion architecture. Generally, receivers may receive unwanted input signals having relatively large power from different sources.
In FIG. 2, the receiver 104 may receive signals having different frequencies and amplitudes via the antenna 106. For example, the receiver 104 may receive wanted signal 108 having frequencies in the desired frequency band. Additionally, the receiver 104 may receive unwanted or interfering signals called blockers. Blockers may be of two types: in-band blockers 110 that have frequencies in the desired frequency band and out-of-band blockers 112 that have frequencies outside the desired frequency band. The power of the blockers 110, 112 may be greater than the power of the wanted channel 108. Consequently, the blockers 110, 112 may generate unwanted intermodulation components when received by the receiver 104.
Additionally, signals transmitted by the transmitter 102 may be a source of blockers in some systems. For example, in wideband code division multiple access (WCDMA) systems, RF transceivers may comprise RF front-end modules that include duplexers. The RF transceivers may simultaneously transmit and receive data using the duplexers.
In FIG. 3A, a WCDMA transceiver 100-1 may comprise an RF front-end module 114, an RF downconverter module 116, and the transmitter 102. In some implementations, the RF front-end module 114 may comprise filter circuits and may be implemented external to an RF transceiver 100-2 as shown in FIG. 3B.
In FIGS. 3A and 3B, the RF front-end module 114 may communicate with the antenna 106, the RF downconverter module 116, and the transmitter 102. The RF downconverter module 116 may include mixers (not shown) that downconvert the RF signals received from the antenna 106. The RF front-end module 114 may comprise filters, amplifiers, etc. that the receiver 104 and/or the transmitter 102 may utilize. Accordingly, the receiver 104 may include the RF downconverter module 116 and a portion of the RF front-end module 114 that the receiver 104 may utilize.
In FIG. 3C, the RF front-end module 114 may comprise a duplexer 120 and a power amplifier 122. The RF transceiver 100-2 may simultaneously transmit and receive data via the duplexer 120. The power amplifier 122 may amplify signals output by the transmitter 102. When the RF transceiver 100-2 transmits data, the duplexer 120 may output the amplified signals received from the power amplifier 122 to the antenna 106.
When the RF transceiver 100-2 receives data, the duplexer 120 may receive RF signals from the antenna 106 and may output the signals received from the antenna 106 to the RF downconverter module 116. Additionally, the duplexer 120 may inject residual signals, which are attenuated portions of the amplified signals output by the power amplifier 122, into the RF downconverter module 116.
Despite being attenuated, the residual signals may have a power level significantly greater than the power of the wanted channel received from the antenna 106. Consequently, the residual signals may appear as large blockers at the input of the RF downconverter module 116 resulting in the generation of unwanted intermodulation components in the RF downconverter module 116.